Experimental and numerical study of thermoforming of Al/CFRP hybrid composites

Composite materials are more and more widely used in the automotive industry with the increasing requirements of lightweight design. In order to obtain automotive parts with excellent comprehensive mechanical properties, the 7075-T6 aluminum alloy was integrated with Carbon Fiber Reinforced Plastic (CFRP) by using thermoforming process. The influence of four forming methods on the forming process, forming accuracy, and interface bonding strength was studied in this work. A finite element model based on cohesion and forming was established to study the integrated thermoforming and properties prediction of Al/CFRP hybrid composites. The results showed that forming CFRP and unformed 7075 Al aluminum alloy sheet together required higher forming energy and the formed parts had higher Mises stresses. When the CFRP was located below 7075 aluminum alloy sheet, the uneven stress distribution due to the severe deformation of the resin resulted in the worst forming accuracy. For all four processes, the thickness of the formed parts decreased at the round corners and side wall area, increased at the flange area, and changed little at bottom surface. The thickness distribution of the formed part depends on the deformation process and the contact pressure between the tools and the blank. Greater contact pressure resulted in greater thinning rate. For the processes of preformed 7075 aluminum alloy, although less forming force was needed, the interface debonding risk between 7075 aluminum alloy and CFRP might arise due to the small contact pressure.